This invention relates to passive structural and aerodynamic control of compressor surge.
When connected to discharge ducting, piping, and volumes, substantially all fluid compressors and pumps can generate pressure oscillations due to instabilities of the pumping system known as surge and stall. The amplitude of these oscillations may be small or large compared to the mean pressure rise in the compressor but, in either case, operation under these conditions is not acceptable due to increased pumping losses and, even more importantly, serious mechanical damage which may accrue. Surge occurs near the maximum pressure the compressor can deliver and thus is often a strict limit to compressor performance. These instabilities are serious problems in such diverse applications as jet engine compressors, automotive turbochargers, gas pipelines, and chemical process plants. Suppression of these instabilities is extremely important because they stand as limits to the performance of all turbomachine pumping systems. Increased stability can be directly translated into a large increase in machine performance--operating range and pressure rise--for essentially any compressor or pump to which it might be applied.
Because of its importance, the control of surge and stall has been explored over the past twenty years. The aim of past research was to realize an increase in average performance by reducing the steady state surge margin, detecting the onset of rotating stall or surge, and then backing off the compressor operating point (lowering its pressure rise) when required, thus trading performance for stability. The approach taken was largely empirical and did not prove totally successful, mainly due to problems associated with detection of the onset of the instability and with the necessity for large control forces required to move the compressor operating point. Active suppression of compressor instabilities has also been proposed. See, "Active Suppression of Compressor Instabilities" AIAA 10th Aerocoustics Conference, Jul. 9-11, 1986, Seattle, Wash. This paper discussed active control of a moving plenum wall to damp surge and suggested, without analysis, that the motions of the plenum wall could be driven by fluctuations in plenum pressure rather than by an active external control. The present invention is directed at suppressing surge in compressor pumping systems using structural and fluid dynamic feedback.